This invention relates to a process for the fabrication of a semiconductor die.
In a conventional process for fabricating semiconductor dies, a semiconductor wafer is processed to form a plurality of circuits on the top side of the wafer, and in later steps, the wafer is separated into individual dies along prescribed dicing streets or lines, each having at least one circuit on its top side. The individual dies are used in semiconductor packages or on circuit boards and are attached to their substrates by adhesive. In addition to the usual semiconductor circuitry on the wafers, some wafers are fabricated with through-silicon-vias, micro bumps and other fabrication elements.
Miniaturization and slimming of electrical and electronic equipment has led to a need for thinner semiconductor dies. One way to produce thinner semiconductor dies is to remove excess material from the back side of the wafer, the side without any circuitry, before the wafer is separated into the individual dies. This removal is typically done by a grinding process and is known as back side grinding, although it can be anticipated that methods other than grinding might be used. After grinding, the thin wafers are then singulated into individual dies, either by mechanical or laser sawing. For very thin wafers (<50 um), there are potential problems with this standard process. Very thin wafers are brittle and tend to warp. In addition, sawing such thin wafers may result in back side or front side chipping, or side wall cracking.
It is more efficient to apply the adhesive for attaching the individual dies to substrates at the wafer level, rather than to the individual dies. Thus, in one fabrication method, the adhesive is applied to the back side of the wafer and is known as a wafer back side coating adhesive.
In order to prevent the cracking of thinned dies during the dicing operation, dicing lines may be partially cut or lasered into the top side of the full thickness wafer between adjacent circuits for the purpose of facilitating later singulation. After the dicing lines are partially cut, a protection tape (also known as a back grinding tape) is laminated to the top side of the wafer to protect the circuitry, and material from the back side of the wafer is removed to the level at which the dicing lines were cut. Once the protection tape is removed, this process results in singulated dies without the need for dicing the thinned wafers, and is known as dicing before grinding.
One drawback to this process is that wafer applied adhesives, such as film, may need further dicing once they are applied to the back of the wafer, which has already been singulated into individual dies. Alternately, if a wafer backside coating adhesive is applied, the coating will enter and contaminate the dicing lines or streets, interfering with the separation process and potentially contaminating the front side of the chips. This creates a need for a means of preventing contamination of the wafer back side coating into the dicing lines between the circuits if a partial dicing operation is done before the grinding down operation to thin the wafer.